Problem with ATX Power Supply

Problem with ATX Power Supply

Ive done the usual and converted a 500W ATX power supply with the intention of running 2 x Turnigy Accucel 6's.

Heres my issues, any help would be appreciated.

Ive got two 12v outputs. The power supply has 2 x 12v rails each capable of 20A with a combined 406W max output. The power supply works fine UNTIL I charge a 6S 5000mah pack. It will not charge above 2.2Amps. When you begin the charging cycle it climbs to 2.2Amps and sits there perfectly (Cells at 3.6v approx). If I charge a 4S 3600 pack I can get it to go above 2.2A (Up to 3.6 I have seen eben though its almost charged). It does this regardless of using balance, normal or quick charge settings.

The output of the power supply during charge shows 11.6V. Im using a 10W 15 ohm power resistor on the RED 5.5v line to provide load and (what I thought) would bring the voltage up.

Ive also connected the brown 3.3sense wire to the orange 3.3v bundle. It seems even if I disconnect this theres no change to the operation of the supply.

Am I doing something wrong.

I thought by splitting the 12v output might be causing an issue but if i connect both rails I still only get 2.2Amp output on the 6s pack ??????

I cant figure this out, what am I doing wrong that wont allow me to draw 5 amps from the supply or is it the charger ? Looking through the Accucel manual I cant see anything Im doing wrong.

Re: Problem with ATX Power Supply

Posted: Thu Aug 16, 2012 4:53 am

by Airbus330

Im an idiot !

Ohms law

W=V x I=22.2 x 2.2=48.84 Watts

I guess Im limited by the 50W max charger output

Charging anything over 2.2Amps would exceed the chargers capacity

Comments ?

Re: Problem with ATX Power Supply

Posted: Thu Aug 16, 2012 6:03 am

by Airbus330

Anu ideas how I can get the voltage up to 12.5 - 13

Thanks

Re: Problem with ATX Power Supply

Posted: Sun Aug 19, 2012 10:08 pm

by chrisjunkie

Voltage will not be easily increased as PCs rely on a very steady 12v.

You're better off almost getting a dumb car charger that will provide ~14v and 3amp output and use that.

Regardless you wont be able to charge your 6S any faster as this is a limit of your charger

Re: Problem with ATX Power Supply

Posted: Mon Aug 20, 2012 10:29 pm

by Oldiron

If a power supply is regulated to a specific voltage as your ATX is you can only change that voltage by replacing components in the regulating circuit. Not impossible but without a schematic or an engineering degree nearly so. Switching power supplies that computers use are not easy to convert to a variable output. Your best bet is to start trolling eBay for a used lab power supply. The automotive type chargers are current regulated and can smoke things that are not as rugged as a lead acid battery and lead acid batteries are VERY rugged! As an example I have used automotive battery chargers as welders when in a pinch.